1. Field of the Invention
The present invention relates to an image processing system configured to perform image processing with an input device and any of a plurality of output devices on a network operating in cooperation with each other.
2. Description of the Related Art
Conventionally, a range of a color space in which a color is reproduced differs with respect to image output devices (e.g., color printers) according to characteristics of the image output devices (i.e., characteristics of ink or toner and a recording method).
FIG. 16 illustrates an area characteristic of a color space related to color reproduction characteristics of an image output device. Here, “x” and “y” are chromaticity coordinates. Chromaticity coordinates are often used in expressing a color reproduction range of a color device in a two-dimensional area.
Referring to FIG. 16, areas illustrated with solid or broken line polygons each indicate an area for reproducing a color with respect to each of color printers A, B, and C.
As apparent from FIG. 16, the color reproduction ranges are from larger to smaller in the order of the printer A, the printer C, and the printer B. Furthermore, the color reproduction range of the printer A includes that of the printer B. That is, the printer A can reproduce all of the colors that the printer B can reproduce.
FIG. 17 illustrates a structure of a profile of an image output device. More specifically, FIG. 17 illustrates an example of a printer profile structure according to profile specifications defined by the International Color Consortium (ICC).
The profile in FIG. 17 includes a header portion for managing the profile, a tag table including a pointer for accessing tag data, and a tag data storage portion including a required tag, an optional tag, and a private tag.
The header portion includes device information and color management module (CMM) information. The device information describes information about which device (e.g., a monitor) the profile corresponds to. The CMM information describes information about which CMM uses the profile. The tag data storage portion includes profile description information for identifying the profile.
The profile description information can be described as, for example, “CXXXXLBP-2XXXX”. That is, the profile description information stores information about a manufacturer name and a product name. The required tag includes a color reproduction range tag which describes information about a color reproduction range of a printer.
FIG. 18 illustrates a data structure of the color reproduction range tag in FIG. 17.
Referring to FIG. 18, color reproduction range tag data includes data for checking whether an input of a device-independent color (a Commission Internationale de l'Éclairage (CIE) color system XYZ or a CIE color system LAB (hereinafter referred to as “L*a*b”)) can be output by a specific printer.
In the case of generating data corresponding to a combination of all inputs, the size of the generated data becomes very large. Accordingly, it is necessary to divide a three-dimensional input color space into a plurality of grid points and allocate the data only with respect to each of the grids. With respect to an input that does not correspond to a grid, it is generally necessary to interpolate the non-grid input with data on surrounding grids to obtain an output thereof.
In the example illustrated in FIG. 18, the input L*a*b* is divided into grid points, and each grid point holds data indicating “ON” if the data can be output by a printer or data indicating “OFF” if the data cannot be output by a printer. Data between grid points is interpolated with data on a grid that is vertices of a cube surrounding the data between grid points. Thus, a result “ON” or “OFF” can be obtained with respect to the data between grid points.
FIG. 19 illustrates a color reproduction range checking function of the CMM.
The color reproduction range checking function is a function for determining a level of a quality of an output in the case where red, green, and blue (RGB) data having a characteristic defined by a source profile (a profile of a scanner or a monitor) is input to the CMM; the CMM outputs an output quality level status based on the input RGB data, a source profile, and a printer profile, and the input RGB data is output by a printer having a characteristic defined by the printer profile.
In the case of outputting input RGB data with a printer, the color reproduction range checking function returns a status of a quality level of the output based on the source profile information and the color reproduction range tag data in a printer profile.
FIG. 20 illustrates an example of processing performed with the color reproduction range checking function in FIG. 19.
Referring to FIG. 20, input RGB data is converted into L*a*b* data based on information included in a source profile (in the example in FIG. 20, based on data used for converting RGB data into L*a*b* data in a device-independent color space)
Then, the converted L*a*b* data is input to the printer, and if it is determined, based on the color reproduction range tag data in the printer profile, that the acquired output quality level status of the printer indicates that the converted L*a*b* data can be output, then the input L*a*b* data is output by the printer.
As described above, it can be determined whether color data can be output by a printer after checking an output quality level status of the printer based on color reproduction range tag data included in a printer profile.
In the case where a user selects either one of a plurality of color printers on a network in a network printing system to output data with the selected color printer, the data may not be printed with the selected printer if the size of the data to be printed is very large or if an error occurs during the print processing. In this regard, Japanese Patent Application Laid-Open No. 11-305970 discusses a method for allowing a user to select a substitute output device, based on a result of a determination as to an output level of a network printer performed according to color reproduction information, in order to correspond to a difference in color reproduction ranges of printers on the network.
Furthermore, another conventional method corrects a gradation to reproduce appropriately colors in an output of a color printer without being influenced by surrounding environments or aging of a printing mechanism.
A method for correcting a gradation in a conventional method will be described below with reference to FIGS. 21 and 22. FIG. 21 illustrates a density characteristic of an output unit of an image forming apparatus.
In FIG. 21, an output density is taken on the ordinate axis. On the ordinate axis, an output density value “0” corresponds to white, and an output density value “255” corresponds to black. A value of data input to the output unit of the image forming apparatus is taken on the abscissa axis. On the abscissa axis, an input data value “0” corresponds to white, and an input data value “255” corresponds to black. A broken line 1400 in FIG. 21 indicates an ideal linear density characteristic. The density characteristic line 1400 indicates that if linear data is input, the density characteristic after printing out the input data becomes linear.
However, the output unit is subject to an influence of an environment and a frequency of use. Accordingly, the density characteristic of the output unit can vary as indicated by curves 1401, 1402, and 1403. In order to achieve a linear output density characteristic, it is necessary to correct density data using a gradation correction table.
FIG. 22 illustrates an example of a gradation correction table used for correcting the non-linearity of the density characteristic illustrated in FIG. 21.
In FIG. 22, ordinate and abscissa axes are similar to those in FIG. 21. A characteristic 1501 is used for correcting the density characteristic 1401. The characteristic 1401 and the characteristic 1501 are symmetrical with respect to a linear density characteristic broken line 1500.
A characteristic 1502 is used for correcting the density characteristic 1402. A characteristic 1503 is used for correcting the density characteristic 1403.
The gradation correction table includes values for the characteristics 1501, 1502, and 1503. Using the gradation correction table, output data can be linearly corrected.
Several conventional methods have been used for calculating density characteristics of an output image illustrated in FIG. 21. For example, a conventional gradation correction method corrects a gradation by performing a gamma correction using a two-dimensional gradation correction table generated for each of yellow (Y), magenta (M), cyan (C), and black (K) to obtain predetermined density characteristics, based on monochromatic gradation patches for colors of Y, M, C, and K printed output in a sample chart and read with a reading unit (reader).
A recent image forming apparatus includes a plurality of image processing methods and halftone processing methods. Thus, a density characteristic of an image digitized by an error distribution method differs from a density characteristic of an image digitized by a screen conversion or dithering. Accordingly, it is necessary to perform a density correction using the above-described gradation correction table for each halftone processing method.
Recent communication lines allow high-speed data communication and a large amount of data communication. In this regard, a method has been used for performing a copy operation, a send operation, or a facsimile transmission operation with network-connected apparatuses, such as a multifunction peripheral (MFP), a printer device, and a scanner device.
In such a method, a user can designate a printer device installed at a location distant from an installation location of a scanner device. Then, image data input by the scanner device can be output to the printer device. Thus, a copy operation can be performed via a network.
However, a conventional network copy method using network-connected apparatuses has the following problems.
For example, it is difficult for a user to recognize whether an appropriate output level can be achieved based on a matching status of color reproduction ranges of a scanner device for inputting image data and a printer device for outputting the input image data and to select a most appropriate printer device. In addition, it is difficult for a user to recognize which printer device has a most appropriate color matching status for a scanner device for inputting image data and to select a most appropriate printer device.
Furthermore, it is difficult for a user to determine whether the above-described gradation correction has been properly performed by the printer device for outputting the input image data.
Accordingly, contrary to a user's intention, the input image data may be output by an output device that has a low color matching status for an image input device, thus resulting in a print product having a low output quality.